ovl: decode lower non-dir file handles

Decoding a lower non-dir file handle is done by decoding the lower dentry
from underlying lower fs, finding or allocating an overlay inode that is
hashed by the real lower inode and instantiating an overlay dentry with
that inode.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/export.c

@@ -169,16 +169,16 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
 				       struct dentry *upper,
 				       struct ovl_path *lowerpath)
 {
-	struct inode *inode;
+	struct dentry *lower = lowerpath ? lowerpath->dentry : NULL;
 	struct dentry *dentry;
+	struct inode *inode;
 	struct ovl_entry *oe;
-	void *fsdata = &oe;
 
-	/* TODO: obtain non pure-upper */
-	if (lowerpath)
+	/* TODO: obtain an indexed non-dir upper with origin */
+	if (lower && (upper || d_is_dir(lower)))
 		return ERR_PTR(-EIO);
 
-	inode = ovl_get_inode(sb, dget(upper), NULL, NULL, 0);
+	inode = ovl_get_inode(sb, dget(upper), lower, NULL, !!lower);
 	if (IS_ERR(inode)) {
 		dput(upper);
 		return ERR_CAST(inode);
@@ -189,11 +189,16 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
 		dentry = d_alloc_anon(inode->i_sb);
 		if (!dentry)
 			goto nomem;
-		oe = ovl_alloc_entry(0);
+		oe = ovl_alloc_entry(lower ? 1 : 0);
 		if (!oe)
 			goto nomem;
 
+		if (lower) {
+			oe->lowerstack->dentry = dget(lower);
+			oe->lowerstack->layer = lowerpath->layer;
+		}
 		dentry->d_fsdata = oe;
+		if (upper)
 			ovl_dentry_set_upper_alias(dentry);
 	}
 
@@ -381,7 +386,14 @@ static struct dentry *ovl_get_dentry(struct super_block *sb,
 	struct ovl_fs *ofs = sb->s_fs_info;
 	struct ovl_layer upper_layer = { .mnt = ofs->upper_mnt };
 
-	/* TODO: get non-upper dentry */
+	/*
+	 * Obtain a disconnected overlay dentry from a disconnected non-dir
+	 * real lower dentry.
+	 */
+	if (!upper && !d_is_dir(lowerpath->dentry))
+		return ovl_obtain_alias(sb, NULL, lowerpath);
+
+	/* TODO: lookup connected dir from real lower dir */
 	if (!upper)
 		return ERR_PTR(-EACCES);
 
@@ -423,6 +435,25 @@ static struct dentry *ovl_upper_fh_to_d(struct super_block *sb,
 	return dentry;
 }
 
+static struct dentry *ovl_lower_fh_to_d(struct super_block *sb,
+					struct ovl_fh *fh)
+{
+	struct ovl_fs *ofs = sb->s_fs_info;
+	struct ovl_path origin = { };
+	struct ovl_path *stack = &origin;
+	struct dentry *dentry = NULL;
+	int err;
+
+	err = ovl_check_origin_fh(ofs, fh, NULL, &stack);
+	if (err)
+		return ERR_PTR(err);
+
+	dentry = ovl_get_dentry(sb, NULL, &origin);
+	dput(origin.dentry);
+
+	return dentry;
+}
+
 static struct dentry *ovl_fh_to_dentry(struct super_block *sb, struct fid *fid,
 				       int fh_len, int fh_type)
 {
@@ -440,10 +471,10 @@ static struct dentry *ovl_fh_to_dentry(struct super_block *sb, struct fid *fid,
 	if (err)
 		goto out_err;
 
-	/* TODO: decode non-upper */
 	flags = fh->flags;
-	if (flags & OVL_FH_FLAG_PATH_UPPER)
-		dentry = ovl_upper_fh_to_d(sb, fh);
+	dentry = (flags & OVL_FH_FLAG_PATH_UPPER) ?
+		 ovl_upper_fh_to_d(sb, fh) :
+		 ovl_lower_fh_to_d(sb, fh);
 	err = PTR_ERR(dentry);
 	if (IS_ERR(dentry) && err != -ESTALE)
 		goto out_err;

fs/overlayfs/namei.c

@@ -310,9 +310,8 @@ static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
 }
 
 
-static int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
-			       struct dentry *upperdentry,
-			       struct ovl_path **stackp)
+int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
+			struct dentry *upperdentry, struct ovl_path **stackp)
 {
 	struct dentry *origin = NULL;
 	int i;
@@ -328,7 +327,7 @@ static int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
 	else if (IS_ERR(origin))
 		return PTR_ERR(origin);
 
-	if (!ovl_is_whiteout(upperdentry) &&
+	if (upperdentry && !ovl_is_whiteout(upperdentry) &&
 	    ((d_inode(origin)->i_mode ^ d_inode(upperdentry)->i_mode) & S_IFMT))
 		goto invalid;
 

fs/overlayfs/overlayfs.h

@@ -266,6 +266,8 @@ static inline bool ovl_is_impuredir(struct dentry *dentry)
 /* namei.c */
 int ovl_check_fh_len(struct ovl_fh *fh, int fh_len);
 struct dentry *ovl_decode_fh(struct ovl_fh *fh, struct vfsmount *mnt);
+int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
+			struct dentry *upperdentry, struct ovl_path **stackp);
 int ovl_verify_set_fh(struct dentry *dentry, const char *name,
 		      struct dentry *real, bool is_upper, bool set);
 int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index);